Sen. Tim Johnson will announce his future political plans in South Dakota on Tuesday, and according to a Reuters report, the three-term Democrat will retire.

Johnson will hold a news conference "regarding the 2014 election" at the University of South Dakota in Vermillion — his 1969 alma mater — at 4 p.m. ET, according to a Monday press release from his Senate office.

Republicans are already targeting the Senate seat and have a top candidate in place: Former Gov. Mike Rounds announced his campaign last year. An open seat only makes the race more alluring for Senate Republicans, who need to pick up six seats to win the majority in 2014.

Democrats have a couple of potential candidates considering the race, including former Rep. Stephanie Herseth Sandlin and Johnson’s son, U.S. Attorney Brendan Johnson. Sandlin has several statewide victories under her belt, while Johnson wields a well-known name in South Dakota politics.

Also, a Republican primary could hurt the GOP's chances of picking up the seat. Rep. Kristi Noem — who defeated Herseth Sandlin in 2010 — continues to consider a bid. Conservative activists in the state hope Noem will challenge the former two-term governor, but if she passes, they would likely recruit someone else.